The effects of simulated catch-and-release angling on adult Atlantic salmon (Salmo salar) and their offspring

• Main Author: Papatheodoulou, Magdalene
• Format: Thesis
• Language: English
• Published: 2021
• Subjects: Cromarty; Atlantic salmon; Salmo salar
• Online Access: http://theses.gla.ac.uk/82716/; https://theses.gla.ac.uk/82716/1/2021PapatheodoulouPhD.pdf

Fish, including Atlantic salmon (Salmo salar), are released by anglers after capture as part of a fisheries management tool known as catch and release (C&R) angling. This has been introduced as a conservation measure to try and halt, or even reverse, the continuous decline in Atlantic salmon numbers. Consequently, prespawned salmon may now experience C&R during the freshwater migration to the spawning grounds. Yet, there is still limited information in this area, including how stress from capture prior to breeding can affect not only the fecundity of the parents, but also the phenotype of the offspring. This study explores how two of the main stressors associated with C&R angling, exercise and air exposure, experienced by the parents shortly (5 – 18 days) prior to spawning affect adult mortality, physiology and reproduction. It also investigates the effects of simulated C&R on the early developmental stages of the progeny, as well as examines its influences on key behavioural (risk-taking behaviour, activity, exploration, aggression, and dominance) and physiological (SMR, MMR, AS) traits in offspring. An equal number of male and female wild adult Atlantic salmon were captured using a permanent fish trap, set up by the Cromarty Firth Fisheries, on the river Blackwater, N. Scotland, during their spawning migration. They then experienced one of three disturbance protocols that comprised of exercise (120 s) and air exposure (0, 60, or 120 s) of different duration, similarly to what they would encounter during a C&R angling event. There was also a fourth group present that did not experience any additional disturbance and was therefore used as baseline (control group). Each experimental fish (of either sex) was later mated (using IVF) with a non-experimental counterpart, and the offspring were reared under fixed conditions. Experimental parent mortality was unaffected by the simulated C&R, however the growth rate of the fungus Saprolegnia spp. on the body of the fish increased. Furthermore, males from the treatment group exercise + extended air produced sperm that survived for longer once activated (i.e. had an increased maximum duration of sperm motility). Females that experienced disturbance spawned at the usual time, but with smaller clutches. An increase in egg and fry mortality was noted for the groups whose parents were exposed to air, mostly due to higher mortality during egg shocking (a normal husbandry practice in hatcheries to separate non-viable eggs) and an increase in fry mortality during a 12-day fungal (Saprolegnia spp.) outbreak. Moreover, adults from the most extreme treatment group (exercise + extended air exposure) produced offspring that were smaller at first feeding. As for offspring behaviour, both the activity and exploration of a novel environment were lower in the treatments whose experimental parent was exercised and then air exposed for an extended period. Similar results in exploration were observed by the offspring in the exercise group. Yet, exploration in the most extreme disturbance group was improved as the fish became bigger. Progeny from the same treatments, ‘exercise’ and ‘exercise + extended air’ also displayed higher levels of aggression. Interestingly however, during the dominance trials, both these treatment groups were subordinate to offspring from the control treatment. Fish from the control treatment exhibited dominance over the fish from the disturbed parents during the trials on the first two days, but an absence of clear dominance was observed on the third day. There was no observable difference in dominance status between the treatment ‘exercise’ and ‘exercise + extended air’ treatments. The metabolism of the offspring was only affected in the exercise group, where both the MMR and AS were reduced. These results suggest that stressing the parents shortly before spawning will not affect the timing of the spawning, but it could influence the reproductive success of the parents. Furthermore, it indicates that disturbing the parents, especially air exposing them for more than 60 s, could adversely affect the early developmental stages of the offspring, including those behavioural traits which could influence dispersal and competition from feeding territories, and thus reduce their chances of survival. The results therefore have implications for both the period over which C&R is allowed and the way in which it is implemented by anglers.